Friction stir welding apparatus, system and method

ABSTRACT

A method of performing friction stir welding is provided herein. More specifically, traditional friction stir welding requires a rotatable head that is forced against a plurality of work pieces to bond the same. The rotational and normal forces generated by the friction stir welding tool are generally reacted by a backing plate, anvil, mandrel or other mechanisms, such hardware are subject to the applied forces and are often supported with additional internal supports. Conversely, a method of performing a friction stir weld is described that omits the need for such a backing member and internal supports as it is performed using a self reacting pin tool.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.12/905,200 which was filed on Oct. 15, 2010 now U.S. Pat. No. 8,132,708which is a divisional of U.S. patent application Ser. No. 12/755,171filed on Apr. 6, 2010 which issued as U.S. Pat. No. 7,866,532 on Jan.11, 2011, all of which are incorporated by reference in their entirety.

FIELD OF THE INVENTION

Embodiments of the present invention are related generally to metalfusion using a dynamic weld head to bond arcuate work pieces. Morespecifically, a weld fixture with external support rings holds the workpieces and a self-reacting friction stir welding tool bonds cylindricalshaped work pieces wherein a backing member is not required tocounteract forces generated by the weld tool.

BACKGROUND OF THE INVENTION

Friction stir welding is a beneficial metal bonding technique whereinmaterials such as aluminum 7075, various alloys of aluminum/lithium andother similar materials previously considered to be unweldable, can bebonded. Friction stir welding also forms joints that possess materialproperties similar to those of the parent materials. Further, thistechnique also provides welds with extremely low dimensional distortion.

Unlike fusion welding, in which portions of each work piece being joinedare melted and then resolidified to form a new and different materialstructure in the area of the weld, friction stir welding is a solidstate process. More specifically, bonding is accomplished bysimultaneously stirring, heating and intermixing plasticized materialfrom each work piece across the joint boundary. Friction stir weldinggenerally employs a stepped cylindrical tool having a head pin (alsoknown as a probe) surrounded at its root by a shoulder. The tool isrotated at a precise speed while being pressed against the work piecesat the joint with substantial force, which may up to about 12,000pounds. Friction between the rotating pin and work pieces causeslocalized heating and plasticizing of the material adjacent to the pin.Heating reduces the yield stress of the material properties of theparent material. In operation, contact between the pin and the workpieces generates heat that causes the material to yield, therebyallowing the pin to plunge into the work pieces such that the shoulderof the tool will contact the surface of the work pieces. The materialadjacent to the joint is then blended by translating the spinning toolalong the joint at a carefully controlled rate. To optimize a weldformed by traditional friction stir welding techniques, it is also knownto alter the angle between the shoulder and the surface of the workpieces. As the pin and shoulder spin and move relative to the workpieces the pin and shoulder simultaneously heat and move the work piecematerial from the leading edge of the tool to the trailing edge of thetool. Translation of the tool along the joint may be accomplished bymoving the tool or by moving the work pieces relative thereto.

Propellant tanks for launch vehicles are commonly comprised ofrelatively thin cylindrical bodies with dome-shaped ends. Thecylindrical portions of the propellant tanks are often additionallyreinforced with integrated ribs, isogrids or other types of internalstiffening members. Internal stiffening members are machined in flattank panels that are then bent subsequent to machining to form curvedbarrel panels that are interconnected by longitudinal welds to formcylindrical barrel sections. Two barrel sections are abutted to define acircumferential joint that is welded to form a portion of an elongatedcylindrical propellant tank. The dome shaped ends are welded to the endsof the welded barrel sections to complete the propellant tank. Usuallyat least one dome includes an access opening that permits personnel toenter the completed propellant tanks to facilitate construction, permitinspections, etc.

One advantage of friction stir welding is that it is solid state, i.e.,a weld technique that does not require weld rods and other materialstraditionally used to fill a gap between abutting work pieces. Inaddition, since the work pieces are not brought to a temperature tocause melting of the parent material, cooling and the distortionsassociated therewith are less of a concern. The heat affected zoneassociated with the weld is also decreased since the work pieces do notbecome molten prior to fusing. Furthermore, by reducing the heat neededto fuse the metals, weld porosity is decreased, solid redistribution isdecreased, solidification cracking is decreased, and liquefactioncracking is reduced. Reduction of the afore-mentioned common weldingdrawbacks lead to a low concentration of weld defects overall, whichmakes friction stir welding a very tolerant welding technique and wellsuited for fabricating propellant tanks.

Other advantages of friction stir welding include (i) the formation ofwelds with good mechanical properties, (ii) increased safety in whichdangerous splattering of molten material is eliminated, (iii) costsavings in which no filler or gas is required, (iv) the method is easilyautomated and (v) the welds produced require less post weldingmachining.

One drawback with friction stir welding is associated with theconsiderable force that must be exerted by the stir welding tool on thework piece. More specifically, the work piece must be supported by asuitable backing member such as an anvil, or mandrel in the case ofcircumferential friction stir welding, to counteract the applied forcesby the weld tool. Mandrels also help prevent geometrical mismatchbetween the work pieces being joined. Thus, when welding propellanttanks, the backing member must be located inside the tank. Without theuse of a counteracting backing member, tank distortions and inadequateweld penetration can result.

Another disadvantage with friction stir welding is that the end weld isincomplete because a hole associated with the pin remains when thefriction stir welding tool is removed from the joint. This hole must besubsequently plugged by traditional welding techniques or by frictionstir plug welding techniques that employ a push or pull plug.

It is a related disadvantage of friction stir welding that the backingmember must be removed after welding is completed. After welding of aclosed vessel such as a tank, access to the interior of the welded tankis often limited. In some instances, access doors or hatches areprovided that give access into the welded tank, but often thesepenetrations are typically small to facilitate proper closing of thetank. Accordingly, heavy duty backing mandrels must often be removedfrom very small openings in the tank, an operation that is verydifficult and time consuming. Further, any contact between the backingtools and the tank may cause damage requiring expensive retesting andrequalification of the propellant tank. Finally, working inside a tankinvokes certain OSHA regulations related to the working in closedenvironments. For example, regulations may require the use of breathingapparatus or a flow of oxygen and a confined spaces permits may berequired. These measures obviously increase the cost of performing theweld operation.

Friction stir welding is described in various patents. For example, U.S.Pat. No. 5,460,317 discloses a rotating tool that is used to create heatsufficient to fuse adjacent work pieces. For example, U.S. Pat. No.5,813,592 to Midling et al., describes friction stir welding of plates.U.S. Pat. No. 4,063,676 to Lilly discloses circumferential friction stirwelding wherein an expanding plug is mounted to a mandrel positionedwithin a tube or a pipe. U.S. Pat. No. 6,247,634 to Whitehouse describesfriction stir welding of a tank wherein an anvil assembly is positionedwithin the tank to resist the force of the pin. U.S. Pat. No. 7,441,686to Odheima et al., discloses a method of friction stir welding employinga backing member. U.S. Pat. No. 5,697,511 to Bampton teachescircumferential friction stir welding that employs a support structure.U.S. Pat. No. 6,070,784 to Holt et al., discloses a method ofcircumferential friction stir welding that uses internal supports. U.S.Pat. No. 6,257,479 to Liwiniski et al., discloses the method of frictionstir welding of pipes that employs a backing tooling apparatus. Finally,U.S. Pat. No. 5,794,835 to Coloigan et al., discloses a traditionalfriction stir welding tool. One skilled in the art will appreciate uponreview of the foregoing prior art that each require a backing anvil orother tools resist the force applied by the friction stir welding tool.

Thus, there is still a need in the field of welding to provide afriction stir welding tool that can be used to join cylindrical workpieces wherein a backing member is not required. The followingdisclosure describes an improved circumferential friction stir weldingsystem and method that do not require a backing member and is ideal tojoin barrel sections of a booster rocket.

SUMMARY OF THE INVENTION

The present invention provides an apparatus, system, and method ofwelding two cylindrically-shaped members. One embodiment of the presentinvention employs friction stir welding wherein a tool is rotated andmoved relative to a joint defined by abutting work pieces. As the toolis moved relative to the work pieces (or vice versa), material isfrictionally heated and plastically transitioned, i.e., stirred, to fusethe work pieces. Although one skilled in the art will appreciate thattraditionally friction stir welding has been used with respect tometallic materials, it could be used to join other materials, such asheavy duty plastics, for example. In one embodiment of the presentinvention the work pieces are comprised of aluminum 2014 at about 0.41inches thick or greater wherein an internal mandrel is not required, asdescribed in further detail below.

Apparatus for Performing Circumferential Friction Stir Welding withoutan Internal Mandrel.

One embodiment of the present invention employs a series ofexternally-situated rings and associated tools. The rings stiffen theexterior of the circumferential barrel sections adjacent to the jointwith the rotating friction stir welding tool therebetween. The ringsprovide a support that helps counteract loads generated by the frictionstir welding tool that are not counteracted by the internally-situatedshoulder. The rings also help secure the work pieces relative to eachother prior to and during welding, and thus minimize misalignmentbetween the work pieces to facilitate the creation of a high strengthweld. The rings may include external adjustments that remove mismatchbetween the work pieces that may be apparent when a backing member isnot employed. Further, the external tooling also acts as a heat sinkthat draws heat from the joint, thereby reducing the heat affected zone.

It is yet another aspect of the present invention to provide anapparatus for maintaining and selectively altering work pieces beingbonded by friction stir welding, wherein the work pieces are abutted toform a seam. This system comprises a first ring assembly and a secondring assembly. The first ring assembly is positioned on one side of theseam and includes an inner ring interconnected to an outer ring by wayof a center ring, a plurality of clamp assemblies interconnected to afirst surface of said center ring, and a plurality of platesinterconnected to a second surface of said center ring. The second ringassembly is positioned on one side of the seam opposite from said firstring assembly and includes an inner ring interconnected to an outer ringby way of a center ring, a plurality of clamp assemblies interconnectedto a first surface of said center ring, and a plurality of platesinterconnected to a second surface of said center ring.

One embodiment of the present invention employs a self-reacting pin toolthat is used to weld work pieces of constant or tapered thicknesses.Preferably, the tool consists of two shoulders with a pin therebetweenwherein an outer shoulder is situated on an outer portion of the workpieces and an inner shoulder is situated on an inner portion of the workpieces. To accommodate the curvature of the work pieces, the innershoulder often has a tapered or rounded edge. The shoulders tightlyengage both opposite surfaces of the work pieces so that forces appliedby each shoulder are generally cancelled. In addition, since twoshoulders are used to generate heat, tool rotation speed can be reduced.More specifically, convention friction stir welding tools generateforces in the 10,000 to 20,000 lb range but as the self-reacting tool ofembodiments of the present invention employs opposing shoulders, theforge forces are typically about 2000 to 4000 lb.

By alleviating some, if not all of the inwardly directed normal forcegenerated by the tool, no backing member or any other internal toolingis needed to stabilize the work pieces during joining is required,tooling cost is reduced, safety is increased, occurrences of tank damageare reduced, and time associated with welding of a propellant tank isreduced. In addition, since the self reacting pin tool completelypenetrates the work pieces being joined, the finished weld spans theentire thickness thereof and weld cracking is reduced. Further, frictionstir welding with a self-reacting pin tool may be used to join membersusually bonded with traditional techniques where the geometry of thework pieces prevents the use of a backing member. That is, innershoulder may be adapted to fit into tighter spaces, thereby makingfriction stir welding feasible for applications previously relegated totraditional welding techniques.

Method of Circumferential Friction Stir Welding without Using anInternal Mandrel.

In another aspect of the present invention, a circumferential frictionstir weld method is provided that omits the need of an internal mandrel,backing anvil or any other internal backing member or mechanism tostabilize the work pieces (hereinafter “backing member”) being bonded orto counteract loads generated by the friction stir welding tool.

A method is provided for performing circumferential stir welding withoutan internal mandrel or any internal support for the hardware. Thismethod employs the first ring assembly and the second ring assemblydescribed above. In operation a first plate having an arcuate outersurface and a first end is aligned with a second plate having an arcuateouter surface and a second end, wherein the outer surface of said firstplate and said second plate are situated such that said first end andsaid second end are abutted to form a seam. The first ring assembly isthen located adjacent to the first end and the second ring assembly islocated adjacent to the second end, wherein the first ring assembly isspaced from the second ring assembly with said seam therebetween. Thering assemblies omit the need for internal supports and provide all thesupport needed direction normal of the plate outer surfaces. Onecontemplated method further includes creating a bore in the first plateand the second plate wherein a portion of the bore is intersected by theseam and placing a pin of a rotating tool within the bore. The tool isforced onto the first plate and the second plate wherein the forceapplied is reacted only by at least one of the first ring assembly andthe second ring assembly. The tool is then rotated and translated withrespect to the first plate and the second plate to form a weldtherebetween. After the weld is completed, the pin is removed from theseam and the associated hole is plugged.

Method of Creating Tack Welds for Circumferential Friction Stir Welding.

It is another aspect of the present invention to provide a method offriction stir welding that employs tack welds. Tack welds are commonlyused to prevent movement of the work pieces prior to welding. In thepresent invention, tack welds are of such a size and thickness that theybreak when in close proximity as the friction stir weld tool approacheseach tack weld. Tack welds are formed at predetermined locations (oftenin a star pattern, for example) about the joint and help preventhardware movement and mismatch during the friction stir weld process.Tack welds temporarily hold the work pieces together so that the primaryweld can be properly formed. In the present invention, tack welds aresuch a size and thickness that they break when in close proximity to thefriction stir welding tool as it approaches each tack weld. For example,a plurality of tack welds are created about the circumference of thebarrel section. After the last tack weld is formed, the tool is engagedin the joint and is moved along the joint to form the primary weld. Asthe tool meets a tank weld it will “unzip” or break the tack welds,thereby re-stirring the metal. That is, when the tool comes in closeproximity of a tack weld, the tack weld is destroyed and replaced by theprimary weld. A major advantage of this process is that adjacent workpieces are sufficiently constrained by the tack welds just prior to thecontemplated weld event. The self-reacting pin tool generates equal andopposite forces that will also align the work pieces to remove mismatchjust prior to being welded. In practice, traditional welding techniquesare used to create the requisite tack welds. Preferably, however, aspecialized friction stir welding pin tool that generates low forgeloads is employed to create the tack welds and thus no backing anvil isrequired. The specialized tool of one embodiment possesses an elongatedpin and a decreased shoulder.

It is another aspect of the present invention to provide a method ofcreating tack welds in a “skip stitch” pattern. A skip stitch pattern ismore specifically described as welding a small continuous portion orlength and then moving the welding tool to another area to create asimilar weld. Typically, the welds are spaced in a star pattern to evenout tolerance differences.

It is yet another aspect to provide a method of creating tack weldsassociated with circumferential stir welding without an internal mandrelor any internal support for the hardware. The contemplated methodemploys the first ring assembly and the second ring assembly describedabove. In operation a first plate having an arcuate outer surface and afirst end is aligned with a second plate having an arcuate outer surfaceand a second end, wherein the outer surface of said first plate and saidsecond plate are situated such that said first end and said second endare abutted to form a seam. The first ring assembly is then locatedadjacent to the first end and the second ring assembly is locatedadjacent to the second end, wherein the first ring assembly is spacedfrom the second ring assembly with said seam therebetween. The ringassemblies omit the need for internal supports and provide all thesupport needed direction normal of the plate outer surfaces. A rotatingtool with an associated pin is spun to a predetermined rate andassociated with a first portion of the seam, which is comprised offorcing the tool onto the first plate and the second plate wherein theforce is reacted only by at least one of the first ring assembly and thesecond ring assembly. The tool is forced onto the first plate and thesecond plate wherein the force applied is reacted only by at least oneof the first ring assembly and the second ring assembly. As one of skillin the art will appreciate the tool is then rotated and translated withrespect to the first plate and the second plate to form a weldtherebetween. The pin is then removed from the seam and moved to asecond portion of the seam and the process is repeated.

Apparatus for Forming Friction Stir Welding Using Tack Welds prior toForming a Circumferential Weld.

It is yet another aspect of the present invention to provide anapparatus for performing friction stir weld tacking that is used withoutan internal mandrel. The tool includes an elongated tip to increasepenetration into the joint and a small shoulder. The small shoulderproduces less load wherein an internal mandrel is not required. The tiplength and decreased shoulder size will produce the requisite heat andmixing to temporarily fuse the work pieces without producing forge loadsthat would create work piece mismatch.

As mentioned, the primary weld will is interrupted by a single holeassociated with the removal of the pin that is subsequently plugged byknown techniques. One solution employs a pull plug having an enlargedend with a shaft extending therefrom. The shaft is placed in the holeleft by the tool wherein the enlarged end positioned within thecylindrical work piece. The plug is then spun and pulled from the weldedtank, thereby securing the plug in the hole. The shaft is then trimmedand the area is planished.

One embodiment of the present invention employs a traditional fixed pintool design that produces reduced loads as described above. These lowloads help reduce the amount of mismatch and deflection that generallyoccurs when attempting to use a traditional friction stir weld tool on acircumferential tack weld with a backing anvil or member. Friction stirwelding or other welding techniques may be used to form the tack weldsas well but may require internal backing to react the loads associatedtherewith.

It is therefore another aspect of the present invention to provide asystem for maintaining and selectively altering work pieces being bondedby friction stir tack welding with a rotating pin tool. The contemplatedmethod employs the first ring assembly and the second ring assemblydescribed above. The apparatus uses a rotating tool for engagement intothe seam, wherein the tool includes a shoulder with a pin extendingtherefrom.

OTHER ADVANTAGES OF EMBODIMENTS OF THE PRESENT INVENTION

It is another aspect of the present invention to provide a system thatincreases the amount of circumferential friction stir welds used in anobject to be welded, without the associated costs associated therewith.For example, such a system relieves manpower associated with a weldingtask by removing the need to move tooling, backing members, etc. Morespecifically, in the realm of launch vehicle production, propellanttanks are generally comprised of cylindrical barrel segments eachcomprised of longitudinally welded barrel panels. The barrel segmentsare capped by end domes to form a propellant tank. The portions of somepressure-stabilized tanks are joined by resistance welds. Heavier,thicker structurally stable barrel segments must be joined by othertechniques such as arc welding, which requires filler. Typically, abooster segment, which comprises at least two propellant tanks, fourteenor more circumferential welds are required, i.e., between sumps anddomes, domes and skirts, domes and barrels, barrel segments and barrel,segment and barrel and dome. The contemplated apparatus and methodsdisclosed herein may be used to weld more of the circumferential weldsof a booster tank.

It is another improvement of the present invention to provide a systemof increasing weld efficiency. More specifically, with respect tobooster tank construction, the prior art method involves the welding ofbarrel sections in various orientations, which increases the time andcomplexity of fabrication. Generally, barrels that make up the boostertank/propellant tanks are comprised of a plurality of flat panels thatare bent and then welded to form a cylindrical barrel segment. Thelongitudinal welds of the barrel segment are often traditional linearfriction stir welds. Typically, barrel segments, cylindrical skirts, anddome sections are welded in a vertical orientation wherein thecomponents are rotated relative to a traditional welding tool to createportions of the propellant tank. Various skirts, adapters, domes, etc.are also welded in this fashion. The tank portions are welded in ahorizontal orientation wherein the pre-welded assembly is rotatedrelative to the welding tool. Thus, in the prior art, barrel panels arelongitudinally welded in the vertical direction to form the barrelsegments that are reoriented (i.e., longitudinal welds placed generallyparallel to horizontal). The re-oriented barrel segments are thenwelded. These various movements and reorientation procedures increasethe risk of damage and injury, are time consuming, and are costly.

The present invention facilitates welding of a propellant tank bystacking barrel panels, domes, etc., vertically on one rotatablefixture, i.e., a turn table. Stacking the components, or subassembliesthereof, reduces the space required to weld a propellant tank andfriction stir welding circumferential joints is made more feasible.Further, the weight of the stacked components will help maintain thelocation of the work pieces relative to each other and helps preventmovement during welding and/or mismatch. Welding in a vertical positionhelps alleviate other drawbacks such as gravitational related welddeformations. The vertical position also ensures that the weld integrityis consistent around the circumference of the tank. It is a relatedaspect of the present invention to therefore facilitate manufacturing ofa booster tank/propellant tanks wherein a single station may be providedfor preparing, trimming, welding, non destructive inspecting (NRI) andplug welding to close out the friction stir weld.

It should be appreciated that the present invention provides frictionstir welding methods that can be used in various fields. The teachingsherein are applicable to many fields, such as ship building (deckpanels, bulk heads, etc.), railways (high speed train bodies),automotive (sheet metal fusion), aerospace (fuselage fabrication),nuclear energy (waste canisters), oil industry pipes and other pressurevessels. One skilled in the art will appreciate that the methodsdescribed herein may be used equally well in other welding applicationswherein it is desirable to avoid using an internal support, a backinganvil or other tool.

The Summary of the Invention is neither intended nor should it beconstrued as being representative of the full extent and scope of thepresent invention. Moreover, references made herein to “the presentinvention” or aspects thereof should be understood to mean certainembodiments of the present invention and should not necessarily beconstrued as limiting all embodiments to a particular description. Thepresent invention is set forth in various levels of detail in theSummary of the Invention as well as in the attached drawings and theDetailed Description of the Invention and no limitation as to the scopeof the present invention is intended by either the inclusion ornon-inclusion of elements, components, etc. in this Summary of theInvention. Additional aspects of the present invention will become morereadily apparent from the Detailed Description, particularly when takentogether with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention andtogether with the general description of the invention given above andthe detailed description of the drawings given below, serve to explainthe principles of these inventions.

FIG. 1 is a partial perspective view of a traditional friction stirwelding tool bonding two work pieces;

FIG. 2 is a perspective view of an upper ring assembly of the presentinvention;

FIG. 3 is a detail view of FIG. 2;

FIG. 4 is an exploded perspective view of FIG. 2;

FIG. 5 is a perspective view of a lower ring assembly of the presentinvention;

FIG. 6 is a bottom perspective view of a lower ring assembly;

FIG. 7 is a bottom plan view of FIG. 5;

FIG. 8 is an exploded perspective view of a portion of the lower ringassembly;

FIG. 9 is a detailed view of FIG. 5;

FIG. 10 is a perspective view clamp assembly as used in conjunction witha lower ring assembly;

FIG. 11 is a perspective view of a weld fixture of the present inventioncomprising an externally-positioned upper ring assembly and twoexternally-positioned lower ring assemblies interconnected by a linkageand supported by a jack stand;

FIG. 12 is a perspective view of the weld fixture shown in FIG. 11associated with barrel panels;

FIG. 13 is a perspective view of a barrel panel subassembly and domeassembly to be welded;

FIG. 14 is a perspective view of the barrel panel subassembly withinterconnected external ring assembly that positions and retains thedome to the barrel panel subassembly;

FIG. 15 is a perspective view showing a welding system of one embodimentof the present invention;

FIG. 16 is an enlarged detailed view of a lower portion of FIG. 15;

FIG. 17 is an enlarged detailed view of the weld head and associated pinengaged on a circumferential joint wherein the work pieces are supportedby rings having finger clamps;

FIG. 18 is an enlarged elevation view of a self reacting pin tool usedin the welding system;

FIG. 19 is a cross-sectional representation of a prior art friction stirweld that requires a backing anvil;

FIG. 20 is a cross-sectional representation of a circumferentialfriction stir weld formed by the tool of FIG. 18;

FIG. 21 is a perspective view showing another welding system of thepresent invention located adjacent to a dome and a sump;

FIG. 22 is a representation of a tack weld formed in accordance with thepresent invention; and

FIGS. 23A and 23B are views of a pin employed to create a tack weld inaccordance with the invention.

To assist in the understanding of the present invention the followinglist of components and associated numbering found in the drawings isprovided herein:

# Component 2 Work piece 6 Joint 10 Welding head 14 Shoulder 18 Pin 22Rotation 26 Force 30 Direction of travel 34 Backing bar 38 Leading edge42 Trailing edge 46 Weld nugget 50 Thermo mechanically affected zone(TMAZ) 52 Unaffected material 54 Heat affected zone (HAZ) 58Self-reacting pin tool 62 Top shoulder 66 Bottom shoulder 70 Nut 74 Weldfixture 78 Upper ring assembly 82 Lower ring assembly 86 Linkage 90 Jackstand 94 Skirt 98 Barrel segment 102 Turn table 106 Spacer 110 Upperring segment 114 Lifting assembly 118 Capture hook 122 Center ring 126Outside ring 130 Inner ring 134 Padding 138 Gusset plate 142 Segmentclamp 146 Riser plate 150 Lower ring segment 154 Jack extenders 158Center ring 162 Inner ring 166 Outer ring 170 Padding 174 Clamp assembly178 Gusset plate 182 Push guide 186 Base 190 Swivel clamp 194 Padding198 Dome 202 Welding assembly 206 Sump 210 Tack weld 214 Spiral 218Groove

It should be understood that the drawings are not necessarily to scale.In certain instances, details that are not necessary for anunderstanding of the invention or that render other details difficult toperceive may have been omitted. It should be understood, of course, thatthe invention is not necessarily limited to the particular embodimentsillustrated herein.

DETAILED DESCRIPTION

Referring now to FIG. 1, a prior art friction stir weld technique isillustrated wherein work pieces 2 are abutted to form a joint 6therebetween. A friction stir welding tool includes a head 10 withassociated shoulder 14 and pin 18. In practice, the shoulder 14 isplaced on the work pieces 2 and the pin 18 is placed within the joint 6after sufficient heat is generated by the spinning tool to allowpenetration thereof. The head 10 is then forced downwardly onto the workpieces 2 as indicated by arrow 26 and is transitioned relative thereto30. One skilled in the art will appreciate that the work pieces 2 mayalso move relative to the rotating head 10. The force 26 generated bythe head 10 is reacted by a backing bar 34. As the head 10 is rotatedand moved forward in the direction 30, friction is generated by theshoulder 14 and the pin 18 which keeps the metal of a portion of bothwork pieces 2 such that metal adjacent to a leading edge 38 of theshoulder 14 is moved/displaced to a trailing edge 42 of the shoulder 14.It is important to note that this method does not create a great amountof heat such that the detrimental affects thereof are reduced and workpieces will be comprised of unaffected material 52. The location of thegreatest amount of heat generated forms a weld nugget 46. Adjacent tothe weld nugget 46 is a thermomechanically affected zone (TMAZ) 50 andadjacent thereto is a heat affected zone (HAZ) 54. The heat affectedzone 54 resulting from friction stir welding techniques is a fraction ofwhat it would be using traditional welding techniques, such as tungsteninert gas welding, for example. Again, the backing bar 34 is needed toreact the force 26 generated by the welding head.

Referring now to FIGS. 2-4, details are shown of the upper ring assembly78 of the present invention as showing it is generally circular innature and has a plurality of upper ring segments 110. In order tofacilitate handling of the upper ring assembly 78, a plurality ofselectively interconnected lifting assemblies 114 may be employed. Theupper ring assembly 78 also includes a plurality of capture hooks 118that engage an upper surface of a barrel segment, for example, that areused to facilitate lifting and handling. The upper ring segments 110 aregenerally comprised of a center ring 122 that is sandwiched between anorthogonally oriented outer ring 126 and an orthogonally oriented innerring 130. Padding 134 may be added to the inner ring 130 that engagesthe outer surface of the barrel segment to prevent damage thereto. Thecenter ring 122 adheres to the outer ring 126 and inner ring 130 by wayof a plurality of gusset plates 138 that are welded to the three ringstructure as shown. The ring segments 110 are interconnected by way ofsegment clamps 142 that are also integrated onto the center ring 122.The segment clamps 142 may be associated with riser plates 146 that areinterconnected to the center ring 122 as well. The lifting assemblies114 may be simply an eye for receiving a hook or any other acceptablelifting assembly that facilitates movement and placement of the upperring 78.

Referring now to FIGS. 5-9, the lower ring assembly 82 is shown. Morespecifically, FIG. 13 shows the lower ring assembly 82′ in a standardposition and FIG. 14 shows it in an inverted position 82″. Similar tothe upper ring assembly, the lower ring assembly 82 is comprised of aplurality of lower ring segments 150. Lifting assemblies 114 may also beassociated with the lower ring assembly 82 to facilitate movementthereof. The lower ring segments 150 are interconnected to each othervia a plurality of segment clamps 142. In addition, the lower ringassembly 82 may include jack extenders 154 for engagement with jackstands.

Referring now specifically to FIG. 8, the lower ring segment 150 isshown that is comprised of a center ring 158 that is sandwiched betweenan inner ring 162 and an outer ring 166. Again, padding 170 may beemployed on one side of the inner ring 162 that prevents damage to thetank components. The inner ring 162 also receives a plurality of clampassemblies 174 that will be described in further detail below. Gussetplates 178 may also be added to provide additional stiffness to thesegment 150.

Referring now to FIGS. 9 and 10, the clamp assembly 174 of oneembodiment of the present invention is shown. Here, the clamp assemblies174 are shown interconnected to the center ring 158. The clampassemblies 174 each include a push guide 182 that is selectivelyinterconnected to a base 186 by way of a swivel clamp 190. The pushguide 182 also includes padding 194 for engagement onto an outerdiameter of the tank. In some embodiments the padding 194 is comprisedof rubber, Polytetrafluoroethylene (Teflon®), or any similar materialthat will not damage the work pieces. The padding may also be comprised,at least partially, of a soft metal such as copper or silver that actsas a heat sink that facilitates cooling of the weld and thus enhancesthe weld's properties. The swivel clamp 190 allows translational androtational movement of the push guide 182 to ensure a tight fit betweenthe ring assembly and the work piece. The push guides 182 help ensurethat the work pieces are properly aligned and mismatch is reduced. Morespecifically, the push guides are each selectively adjustable and arecapable of moving the work piece to which they are associated. Forexample, the push guides 182 of one embodiment are capable of minuteadjustments on the order of about 0.001 to 1.0 inches. In one embodimentthe push guide 182 pushes inboard on the work piece that is too faroutboard by rotating a threaded screw on a finger guide that attaches toa finger base and therefore moving the finger guide in or out to adjustthe mismatch. Often a laser measurement device is used to assessmismatches that are addressed prior to or during work piece fusion. Themismatch reduction process can be automated.

Referring now to FIGS. 11-17, a weld fixture 74 of one embodiment of thepresent invention is shown that is comprised of an upper ring assembly78 that is spaced from a plurality of lower ring assemblies 82. A firstlower ring assembly 82′ is connected with the upper ring assembly 78 byway of a plurality of linkages 86. A second lower ring assembly 82″ isspaced from the first lower ring assembly 82′ and is supported by aplurality of jack stands 90. The lower ring assemblies 82′ and 82″ arearranged so that one ring assembly is present on one side of the joint 6and the other ring assembly is placed on the other side of the joint. InFIGS. 12-14, the circumferential joint 6 is formed by mating a skirt 94to a barrel segment 98. In operation, the first lower ring assembly 82′is separated from the second lower ring assembly 82″ that is inverted ascompared to the first lower ring assembly. The skirt 94 ultimately restson a turn table 102. The second lower ring assembly 82″ rests on aplurality of jack stands 90 that are also interconnected to the turntable 102. In operation, a friction stir welding pin tool 58 (See FIG.2) is associated with the circumferential joint 6 while the barrelsegment 98, associated skirts 94, and fixture 74 are rotated relativethereto. The upper ring assembly 78 has a function of supporting thefirst lower ring assembly 82′, but it is not required to perform thecircumferential weld operation. The ring assemblies are comprised ofvarious segments that are engaged onto an outer surface of the barrelsegment 98 or skirts 98 and do not require penetration into thethickness thereof. The use of the previously-described pin tool 58 alsoomits the need for an internal mandrel positioned within the tank.

Referring now specifically to FIGS. 11-14, the upper ring assembly 78 isshown associated with an upper portion of the barrel segment 98. Aplurality of linkages 86 extend downwardly from the upper ring assembly78 and are interconnected to a lower ring assembly 82′. The invertedlower ring assembly 82″ is spaced from the first lower ring assembly82′. The barrel segment 98 rests atop the skirt 94 and is weldedthereto. A circumferential joint (see FIG. 17) is defined by theengagement of the barrel panel onto the skirt 94. A spacer 106 may alsobe used to associate the skirt with the turn table 102. Referring now toFIGS. 19 and 20, the weld fixture 74 of one embodiment of the presentinvention is shown. In operation, a spacer 106 is associated with theturn table 102. A skirt 94 is situated on the spacer 106. Within theskirt 94 resides a dome 198 that includes a lip for engagement with theskirt 94 and a plurality of barrel segments 98. These items are stackedvertically and the ring assemblies are placed around the joints. Theentire assembly, along with the weld fixtures 74 then rotated withrespect to a welding assembly 202 to create the circumferential frictionstir welds. The vertical stacking of the components has advantages overthe prior art described above.

Referring now to FIGS. 17 and 18, a self reacting pin tool 58, alsoreferred to herein as (“pin tool”) is shown. The pin tool 58 isinterconnected to a weld head 10. The pin tool 58 includes a topshoulder 62 that is spaced from a bottom shoulder 66 with a pin 18therebetween. The space between the top shoulder 62 and the bottomshoulder 66 is generally equal to the thickness of the work pieces 2being mated. The pin 18 is adapted to spin and travel along the joint 6between the work pieces 2. The construction of the weld fixturediscussed below, allow external forces and internal forces 26 generatedby the pin tool 58 to counteract each other, thereby omitting the needfor inner internal mandrel. The bottom shoulder 66 is interconnected tothe pin 18 by way of a nut 70 or similar member, and is positionedwithin the interior of the member being welded. Retrieval of the nut 70and bottom shoulder 66 is much easier compared to retrieval of a backingmandrel or internal supports traditionally used because the nut is muchsmaller than large internal supports. As shown in FIG. 2, the joint 6 iscircumferential and is positioned between ring assemblies, which will bedescribed in further detail below. Although a circumferential weld isshown, the use of a self reacting pin tool 58 may find equal applicationin traditional linear friction stir welding operations.

Referring now to FIGS. 19 and 20, the weld nugget 46 is generallyu-shaped and tapers towards the backing anvil 34. Conversely, withreference to FIG. 20, the weld nugget 46 is located generally in thecenter of the work pieces 2 wherein stirring of the parent material hasoccurred completely through the thickness of the abutting edge of theparent materials. Stirring of the parent material in this manner willresult in a complete weld penetration.

FIG. 21 illustrates that the friction stir welding technique describedherein may have applications related to eccentric orientations of workpieces. Here, a sump 206 is welded onto a dome. The interface relatedthereto is neither circumferential nor linear and the weld is beingadded an angle. The circumferential self reacting pin tool may be usedin this situation as well. The dome is spun by another turn tablerelative to the weld assembly. Alternatively, the dome can be help inplace on a fixture and a six-axis friction stir welding tool may beemployed.

Referring now to FIGS. 22 and 23, in order to help hold work pieces 2together prior to and during the creation of the primary weld, aplurality of tack welds 210 are initially created in the joint. The tackwelds 210 are preferably spaced about 8 inches from their center, butmay be spaced any distance apart. Tacking in this manner also helpsprevent mismatches between the work pieces 2.

In one embodiment, the tack welds are formed with a specialized toolthat generates low forge loads. One of skill in the art will appreciatethat the tool shown possesses a small shoulder 14 and lengthen pin 18.The tool shown generates a low forge load while producing an acceptabletack weld. The lengthened pin 18 provides increased penetration and theshoulder 14 provides sufficient mixing to create the tack weld. The toolmay also include a shoulder within a spinal pattern 214 and a conicalpin. The spiral pattern necessarily has a groove 218 that helpsdissipate heat. This new tool achieves a weld that was previouslyachieved with higher forge loads, which required a backing member tocounteract the same.

In operation, subsequent to the creation of a series of tack welds aboutthe circumference of the work pieces, a hole is drilled into the joint.The self reacting pin tool is placed within the hole and the innershoulder thereof is interconnected to the pin. The self reacting pintool is then used to weld the entirety of the circumferential joint 6.When the tool is located proximate to a tack weld 210, the tack 210 weldwill be destroyed in favor of the new primary weld. The head 10 thatcontrols the pin 58 may be automated wherein weld parameters areadjusted during weld development. At the end of the welding process, theinner shoulder of the self reacting pin tool is removed and the pin isremoved from the joint to reveal a single hole that is plugged. Theplugged area, and often the weld in its entirety, is planished orotherwise machined to facilitate inspection thereof.

While various embodiments of the present invention have been describedin detail, it is apparent that modifications and alterations of thoseembodiments will occur to those skilled in the art. Moreover, referencesmade herein to “the present invention” or aspects thereof should beunderstood to mean certain embodiments of the present invention andshould not necessarily be construed as limiting all embodiments to aparticular description. However, it is to be expressly understood thatsuch modifications and alterations are within the scope and spirit ofthe present invention, as set forth in the following claims.

1. A method for performing circumferential stir welding without aninternal mandrel or internal supports, comprising: providing a firstarcuate outer surface; providing a second arcuate outer surface;orienting the first and second arcuate outer surfaces to be stackedvertically with respect to one another; aligning said first arcuateouter surface and said second arcuate outer surface such that an end ofeach is abutted to form a seam; providing a first ring assembly having afirst inner ring, a first outer ring disposed radially outward from thefirst inner ring, and a plurality of first clamp assemblies extendingradially inward beyond said first inner ring; providing a second ringassembly having a second inner ring, a second outer ring disposedradially outward from the second inner ring, and a plurality of secondclamp assemblies extending radially inward beyond said second innerring; positioning said first ring assembly and said second ring assemblyadjacent to said seam, wherein said first ring assembly is spaced fromsaid second ring assembly with said seam therebetween and wherein aninner surface of said first arcuate outer surface and said secondarcuate outer surface are unsupported in a normal direction; providing astand that supports the first and second outer surfaces and the firstand second ring assemblies in a vertical arrangement; creating a bore insaid first arcuate outer surface and said second arcuate outer surfacewherein a portion of said bore is intersected by said seam; placing apin of a rotating tool within said bore; forcing said tool onto saidfirst arcuate outer surface and said second arcuate outer surfacewherein said force is reacted by at least one of said first ringassembly and said second ring assembly and said force is not reactedwith an internal mandrel; rotating said tool; translating said tool withrespect to said first arcuate outer surface and said second arcuateouter surface to form a weld therebetween; removing said pin from saidseam to reveal a hole; and plugging the hole.
 2. The method of claim 1,further comprising rotating said tool; forcing said tool into a firstpoint of seam to operatively contact said first arcuate outer surfaceand said second arcuate outer surface wherein said force is reacted onlyby at least one of said first ring assembly and said second ringassembly; translating said tool with respect to said first arcuate outersurface and said second arcuate outer surface to form a first weldtherebetween; removing said pin from said seam; forcing said tool into asecond point of seam, which is spaced from said first point, tooperatively contact said first arcuate outer surface and said secondarcuate outer surface wherein said force is reacted only by at least oneof said first ring assembly and said second ring assembly; translatingsaid tool with respect to said first arcuate outer surface and saidsecond arcuate outer surface to form a second weld therebetween; andremoving said pin from said seam.
 3. The method of claim 1, furthercomprising associating the pin with said seam a plurality of times tocreate tack welds in addition to said first weld and said second weldsuch that a the circumference of said seam has generally evenly spacedtack welds therearound.
 4. The method of claim 2, wherein said firstweld and said second weld are approximately 4.0 inches in length.
 5. Amethod, as claimed in claim 1, further including: changing a positioningof the first or second arcuate surfaces by adjusting corresponding theclamp assemblies of said first and second plurality of clamp assemblies.6. A method, as claimed in claim 1, wherein: said translating stepfurther includes rotating the first and second ring assemblies relativeto the rotating tool.
 7. The method of claim 5, wherein at least oneclamp assembly of said plurality first and second clamp assembliesincludes a guide for engagement with at least one of said first plateand said second plate by way of an adjustable member associated withsaid at least one clamp.